Retroviral vectors containing cDNAs for the expression of appropriate genes have been proposed or use in correcting an/or alleviating certain human diseases. However, little is known about possible adverse effects of the proposed vectors. In collaboration with scientists at NHLBI, NIH and Genetic Therapy, Inc., we are investigating the ability of retroviral vectors to cause morphological transformation and altered differentiation of mouse embryo C3H/10T-(one-half) cells. In several studies conducted to date, one retroviral vector construct has not been shown to cause the morphological transformation of C3H/10T-(one-half) cells. Further studies to determine possible biological effects of this and other retroviral vectors are in progress.